Where is the command box in the bottom left of the 3D viewport?
This box is called the Operator Panel. It only appears after you perform certain actions, and often &quot;disappears&quot; as soon as you click away from it or you use any kind of transformation (move, scale, rotate, or when you click on another object).
For example, if you add a cylinder (Shift+A &gt; Mesh &gt; Cylinder), before you do anything else, look in the bottom left corner - there will be a little text box that only says &quot;Add Cylinder&quot;. Click this box and it will expand for more options. Once you've expanded it once, it should appear expanded for all actions until you shrink it again (eg: other things you do, like add a loop cut will cause this box to appear &quot;fully opened&quot;). But, it will still disappear when you click away.

Keep your eye out for this box as you perform different actions (both in object and edit mode) - you'll be surprised how much it appears. There are lots of options that you can make use of through this panel.
Alternatively, you can use a floating window with the same options by pressing F9